1. FIELD OF THE INVENTION
This invention relates to document imprinters, especially for tickets, tags, labels, and the like, and particularly to the means for driving the inking roller of such an imprinter.
2. DESCRIPTION OF THE PRIOR ART
In document imprinters of the type having an inking roller, as the machine is used for inking roller tends to shrink because of wear, and/or ink depletion if it is a microporous ink impregnated roller.
For best quality printing, the inking roller is driven by a drive train so arranged that there will be zero relative velocity between the roller and the rotary printing unit at the inking nip. However, as the roller is adjusted closer to the printing unit the drive train component movable therewith is correspondingly moved. This makes it difficult to maintain the same rotational speed of the inking roller, and therefore the desired zero velocity at the inking nip.
If this zero relative velocity is not maintained, the printing type faces will wipe on the inking roller thereby resulting in overinking. If the imprinter is printing conventional, visually readable printing this will not be functionally critical but will result in printed labels having a poor appearance. However, if the imprinter is printing OCR characters, i.e., characters which are visually readable and which are also to be automatically read by optical character recognition equipment, this defect cannot be tolerated. The resulting blurred, non-sharp printing will cause reading errors.